System suitability method for use with protein concentration determination by slope

ABSTRACT

Disclosed are methods of determining the suitability of a variable-length spectrophotometer using Patent Blue dye or AMG Blue dye. Also disclosed herein are methods of determining the suitability of a fixed path length spectrophotometer for determining protein concentration of a protein sample. AMG Blue dye may also be used to determine the suitability of fixed path length spectrophotometers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No. 62/780,184 filed Dec. 14, 2018, which is incorporated herein by reference.

SEQUENCE LISTING

The present application is being filed with a sequence listing in electronic format. The sequence listing provided as a file titled, “A_2335_WO_PCT_sequence_ST25.txt” created Dec. 11, 2019, and is approximately 264,014 bytes in size. The information in the electronic format of the sequence listing is incorporated herein by reference in its entirety.

FIELD

The presented subject matter relaters to the field(s) of protein analysis. Specifically, the presented subject matter relates to determining the suitability of instruments that determine protein concentration.

BACKGROUND

Protein concentration is a critical quality attribute as it directly relates to the dosing of the patient. Established methods for protein concentration determination are based on the compendial method according to Beer-Lambert law of spectroscopy and allows for use of either the conventional fixed path length or variable path length technology.

SUMMARY

1. In a first aspect, disclosed herein are methods of determining the suitability of a variable-length spectrophotometer for determining protein concentration of a protein sample, comprising measuring the absorbance of Patent Blue dye (PBD) or AMG Blue Dye (ABD) at least two wavelengths, the first wavelength of 280 nm and the subsequent wavelength(s) selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm. In a second aspect, disclosed herein are methods of determining the suitability of a fixed path length spectrophotometer for determining protein concentration of a protein sample, comprising measuring the absorbance of AMG Blue Dye (ABD) at least two wavelengths, the first wavelength of 280 nm and the subsequent wavelength(s) selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm. In some sub-aspects or these first two aspects, a third wavelength is used, wherein the third wavelength is different than the second wavelength and selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm. Also in these first two aspects in sub-aspects, the PBD or ABD is measured at the two wavelengths three times for each wavelength before measuring the protein concentration of the protein sample, and wherein the PBD is measured at the two wavelengths three time for each wavelength after measuring the protein concentration of the protein samples. In sub-aspects, the first wavelength is 280 nm and the second wavelength is 310 nm. In some sub-aspects, the variable-length spectrophotometer or fixed path length spectrophotometer is considered suitable if the absorbance readings of the PBD or ABD are equal to or less than 10% of those values supplied in a certificate of analysis supplied with the PBD or ABD. In other sub-aspects, the variable-length spectrophotometer or fixed path length spectrophotometer is considered suitable if the absorbance readings of the PBD or ABD are at least equal to or less than 5% of those supplied in a certificate of analysis supplied with the PBD or ABD. In other sub-aspects, the readings have a relative standard deviation (RSD) percentage of 5%.

In any of these aspects and sub-aspects, the protein sample comprises a therapeutic protein, such as an antigen binding protein, an antibody, a bi-specific antibody, a tri-specific antibody, a BiTE molecule, or a fragment or derivative thereof.

In aspects and sub-aspects directed to variable length spectrophotometers, the variable length spectrophotometer is a SoloVPE spectrophotometer (C Technologies, Inc.; Bridgewater, N.J.). In any of these aspects, AMG Blue dye is preferred to PBD.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows UV absorbance spectrum for Patent Blue dye (PBD).

FIG. 2 shows the raw data obtained in readings of PBD.

FIG. 3 shows the raw data obtained in readings of three protein samples (mAb1 and mAb2, mAb2 at two different concentrations).

FIG. 4 shows graphs of plots of the differences of the reading from the certified values for PBD (as provided by the supplier) at the indicated wavelengths.

FIG. 5 shows a graph of the normal distribution of PBD readings at 280 nm.

FIG. 6 shows a graph of the normal distribution of PBD readings at 310 nm.

FIG. 7 (280 nm) and FIG. 8 (310 nm) show normal bivariate contours of the data set in consideration of the variation or errors associated with the instrument and the reliability of the certified value of the PBD reading

FIG. 9 shows a comparison of protein concentration determination at low concentration (left panel; mAb2) and mid concentration (right panel; mAb2) graphs.

FIG. 10 shows a comparison of PBD at 310 nm (left panel) with protein concentration determinations (mAb1; right panel) graphs.

FIG. 11 shows graphs of a putative wavelength shift for the Cary 60 spectrophotometer impacting the PBD at 280 nm (left), 310 nm (center) and for mAb1.

FIG. 12 shows graphs of a bootstrap analysis for the co-efficient variation o for the three protein concentrations analyzed in the examples.

FIG. 13 shows screen shows for fixed slope mode of the Solo VPE device.

FIG. 14 shows a graph of the UV/Visible spectrum the AMG Blue dye.

FIG. 15 shows the instrument path lengths required for the protein concentration determinations.

DETAILED DESCRIPTION

The Beer-Lambert law is expressed as A=αlc, where A is the measured absorbance, a is the molar absorption coefficient, l is the pathlength, and c is the sample concentration. This equation can be rearranged for use with slope spectroscopy: A/l=αc. For measurements comparing slope and pathlength, a linear regression equation can be written as A=ml+b, where m is the slope of the regression line, and b is the y-intercept. Dimensional equality then allows for replacement of the left-hand side of the second equation above with the slope term from the third equation, yielding the following: m=αc. That resulting equation is the slope spectroscopy equation. It can be used to calculate a sample's if the molar absorption coefficient is known—by dividing it into the slope: c=m/α. If the sample concentration is known, the molar absorption coefficient can be calculated by dividing the slope by the concentration: α=m/c (Huffman et al 2014).

In variable length spectrophotometers, pathlength selection is computer controlled and optimized based on the absorbance achieved. For example, the Solo VPE spectroscopy system (C Technologies, Inc.; Bridgewater, N.J.) is equipped with a computer-controlled linear stage that can determine the absorbance of a sample within the instrument's linear range. It will then generate 5-10 absorbance measurements at successively larger or smaller pathlengths within that linear range. The provided software then calculates and plots a linear regression equation for the resulting absorbance and pathlength data to generate slope, intercept, and R2 values. Then the slope value is used—along with a user-supplied extinction coefficient for the compound of interest—to back-calculate the actual analyte concentration in the sample using the Beer-Lambert law (Huffman et al 2014).

In system suitability assays, which are used to check a system before or during analysis of unknowns to ensure system performance, standards are used.

Definitions

“Patent Blue dye” or PBD means CHEM013 Measurement Standard (SKU CHEM013-KIT; C Technologies, Inc.; Bridgewater, N.J.) or the equivalent. This dye is made to specifications by GFS Chemicals, Columbus Ohio, Item: 8416, called “In-Spec® Patent Blue Color Standard Custom UV-Visible Reference Material.” The composition is 90-100% water, 1-<3% methyl alcohol, and <0.1% Patent Blue Violet (aka Acid Blue 1 and CI 42045 (CAS 129-17-9). The specified wavelength is 310 nm. For the present disclosure, the path lengths are 5 μm to 50 μm path lengths.

“AMG Blue dye” means 0.15% Patent Blue VF in 1× phosphate buffered saline (PBS), 5% glycerol buffer), where the PBS is Dulbecco's PBS without calcium chloride and without magnesium chloride, and the Patent Blue VF is also known as Acid Blue 1, Sulfan Blue and having the empirical formula (Hill notation) of C₂₇H₃₁N₂NaO₆S₂; CAS Number 129-17-9).

AMG Blue dye is preferred in the disclosed and claimed methods.

“Protein”, “peptide”, and “polypeptide” are used interchangeably to mean a chain of amino acids wherein each amino acid is connected to the next by a peptide bond.

“Antibodies” (Abs) and the synonym “immunoglobulins” (Igs) are glycopolypeptides having the same structural characteristics. While antibodies exhibit binding specificity to a specific antigen, immunoglobulins include both antibodies and other antibody-like molecules that lack antigen specificity. Polypeptides of the latter kind are, for example, produced at low levels by the lymph system and at increased levels by myelomas. Thus, the term “antibody” or “antibody peptide(s)” refers to an intact antibody, an antibody derivative, an antibody analog, a genetically altered antibody, an antibody having a detectable label, an antibody that competes for specific binding with a specified antibody, or an antigen-binding fragment (e.g., Fab, Fab′, F(ab′)2, Fv, single domain antibody) thereof that competes with the intact antibody for specific binding and includes chimeric, humanized, fully human, and bispecific antibodies. In some cases, antigen-binding fragments are produced, for example, by recombinant DNA techniques. In other cases, antigen-binding fragments are produced by enzymatic or chemical cleavage of intact antibodies. Antigen-binding fragments include Fab, Fab′, F(ab)2, F(ab′)2, Fv, and single-chain antibodies.

Monoclonal antibodies and antibody constructs include “chimeric” antibodies in which a portion of the heavy and/or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain(s) is/are identical with or homologous to corresponding sequences in antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity. Chimeric antibodies include “primitized” antibodies comprising variable domain antigen-binding sequences derived from a non-human primate (e.g., Old World Monkey, Ape, etc.) and human constant region sequences.

Monoclonal antibodies and antibody constructs include antibodies referred to as “human” or “fully human.” The terms “human antibody” and “fully human antibody” each refer to an antibody that has an amino acid sequence of a human immunoglobulin, including antibodies isolated from human immunoglobulin libraries or from animals transgenic for one or more human immunoglobulins and that do not express endogenous immunoglobulins; for example, Xenomouse® antibodies and antibodies as described by Kucherlapati et al. in U.S. Pat. No. 5,939,598.

“Genetically altered antibodies” means antibodies wherein the amino acid sequence has been varied from that of a native antibody. Because of the relevance of recombinant DNA techniques in the generation of antibodies, one need not be confined to the sequences of amino acids found in natural antibodies; antibodies can be redesigned to obtain desired characteristics. The possible variations are many and range from changes to just one or a few amino acids to complete redesign of, for example, the variable and/or constant region. Changes in the constant region, in general, are made in order to improve or alter characteristics, such as complement fixation, interaction with membranes and other effector functions, as well as manufacturability and viscosity. Changes in the variable region can be made to improve antigen binding characteristics.

A “Fab fragment” is comprised of one light chain and the CH1 and variable regions of one heavy chain. The heavy chain of a Fab molecule cannot form a disulfide bond with another heavy chain molecule.

A “Fab′ fragment” contains one light chain and one heavy chain that contains more of the constant region, between the CH1 and CH2 domains, such that an interchain disulfide bond can be formed between two heavy chains to form a F(ab′)2 molecule.

A “F(ab′)2 fragment” contains two light chains and two heavy chains containing a portion of the constant region between the CH1 and CH2 domains, such that an interchain disulfide bond is formed between two heavy chains.

“Fv fragment” and “single chain antibody” refer to polypeptides containing antibody variable regions from both heavy and light chains but lacking constant regions. Like an intact antibody, an Fv fragment or single chain antibody are able to bind selectively to a specific antigen. With a molecular weight of only about 25 kDa, Fv fragments are much smaller than common antibodies (150-160 kD), and even smaller than Fab fragments (about 50 kDa, one light chain and half a heavy chain).

A “single domain antibody” is an antibody fragment consisting of a single domain Fv unit, e.g., VH or VL. Like an intact antibody, a single domain antibody is able to bind selectively to a specific antigen. With a molecular weight of only 12-15 kDa, single-domain antibodies are much smaller than common antibodies (150-160 kDa) which are composed of two heavy polypeptide chains and two light chains, and even smaller than Fab fragments (about 50 kDa, one light chain and half a heavy chain) and single-chain variable fragments (about 25 kDa, two variable domains, one from a light and one from a heavy chain). Nanobodies derived from light chains have also been shown to bind specifically to target epitopes.

Introduction and Summary of Findings from Examples

System suitability, assay and sample acceptance criteria were established for the determination of protein concentrations involving the variable path length instrument, SoloVPE (C Technologies, Inc.; Bridgewater, N.J.; see also U.S. Pat. No. 7,808,641). Data for the establishment of these criteria were obtained using the SoloVPE at three protein concentrations and bracketed with readings of the PBD. Statistical analyses of these data revealed that ±5% of certificate of analysis (CoA) value at 280 nm and 310 nm were acceptable for use as the system suitability criteria. The precision of the system suitability readings must have a relative standard deviation (RSD) percentage of ≤5% for both beginning and end of the PBD and AMG Blue dye readings. For assay acceptance criteria, this study using the SoloVPE software showed that 36 individual protein readings could be made with consistent inter-sample results. Protein samples should be read in triplicate with a 5% RSD criteria applied.

The concentration of the Patent Blue VF, the pH (see the Examples for suitable buffers) and organic composition of the AMG Blue dye solution are critical attributes of the AMG Blue solution. Implementation of Multi-Mode in the SoloVPE device for the testing greatly simplifies the system suitability procedure while maintaining the sensitivity required for an effective evaluation of instrument performance.

Therapeutic Polypeptides

Proteins, including those that bind to one or more of the following, can be useful in the disclosed methods. These include CD proteins, including CD3, CD4, CD8, CD19, CD20, CD22, CD30, and CD34; including those that interfere with receptor binding. HER receptor family proteins, including HER2, HER3, HER4, and the EGF receptor. Cell adhesion molecules, for example, LFA-I, Mol, p150, 95, VLA-4, ICAM-I, VCAM, and alpha v/beta 3 integrin. Growth factors, such as vascular endothelial growth factor (“VEGF”), growth hormone, thyroid stimulating hormone, follicle stimulating hormone, luteinizing hormone, growth hormone releasing factor, parathyroid hormone, Mullerian-inhibiting substance, human macrophage inflammatory protein (MIP-I-alpha), erythropoietin (EPO), nerve growth factor, such as NGF-beta, platelet-derived growth factor (PDGF), fibroblast growth factors, including, for instance, aFGF and bFGF, epidermal growth factor (EGF), transforming growth factors (TGF), including, among others, TGF-α and TGF-β, including TGF-βI, TGF-β2, TGF-β3, TGF-β4, or TGF-β5, insulin-like growth factors-I and -II (IGF-I and IGF-II), des(I-3)-IGF-I (brain IGF-I), and osteoinductive factors. Insulins and insulin-related proteins, including insulin, insulin A-chain, insulin B-chain, proinsulin, and insulin-like growth factor binding proteins. Coagulation and coagulation-related proteins, such as, among others, factor VIII, tissue factor, von Willebrands factor, protein C, alpha-1-antitrypsin, plasminogen activators, such as urokinase and tissue plasminogen activator (“t-PA”), bombazine, thrombin, and thrombopoietin; (vii) other blood and serum proteins, including but not limited to albumin, IgE, and blood group antigens. Colony stimulating factors and receptors thereof, including the following, among others, M-CSF, GM-CSF, and G-CSF, and receptors thereof, such as CSF-1 receptor (c-fms). Receptors and receptor-associated proteins, including, for example, flk2/flt3 receptor, obesity (OB) receptor, LDL receptor, growth hormone receptors, thrombopoietin receptors (“TPO-R,” “c-mpl”), glucagon receptors, interleukin receptors, interferon receptors, T-cell receptors, stem cell factor receptors, such as c-Kit, and other receptors. Receptor ligands, including, for example, OX40L, the ligand for the OX40 receptor. Neurotrophic factors, including bone-derived neurotrophic factor (BDNF) and neurotrophin-3, -4, -5, or -6 (NT-3, NT-4, NT-5, or NT-6). Relaxin A-chain, relaxin B-chain, and prorelaxin; interferons and interferon receptors, including for example, interferon-α, -β, and -γ, and their receptors. Interleukins and interleukin receptors, including IL-I to IL-33 and IL-I to IL-33 receptors, such as the IL-8 receptor, among others. Viral antigens, including an AIDS envelope viral antigen. Lipoproteins, calcitonin, glucagon, atrial natriuretic factor, lung surfactant, tumor necrosis factor-alpha and -beta, enkephalinase, RANTES (regulated on activation normally T-cell expressed and secreted), mouse gonadotropin-associated peptide, DNAse, inhibin, and activin. Integrin, protein A or D, rheumatoid factors, immunotoxins, bone morphogenetic protein (BMP), superoxide dismutase, surface membrane proteins, decay accelerating factor (DAF), AIDS envelope, transport proteins, homing receptors, addressins, regulatory proteins, immunoadhesins, antibodies. Myostatins, TALL proteins, including TALL-I, amyloid proteins, including but not limited to amyloid-beta proteins, thymic stromal lymphopoietins (“TSLP”), RANK ligand (“OPGL”), c-kit, TNF receptors, including TNF Receptor Type 1, TRAIL-R2, angiopoietins, and biologically active fragments or analogs or variants of any of the foregoing.

Exemplary polypeptides and antibodies include Activase® (Alteplase); alirocumab, Aranesp® (Darbepoetin-alfa), Epogen® (Epoetin alfa, or erythropoietin); Avonex® (Interferon β-Ia); Bexxar® (Tositumomab); Betaseron® (Interferon-(3); bococizumab (anti-PCSK9 monoclonal antibody designated as L1L3, see U.S. Pat. No. 8,080,243); Campath® (Alemtuzumab); Dynepo® (Epoetin delta); Velcade® (bortezomib); MLN0002 (anti-a4137 Ab); MLN1202 (anti-CCR2 chemokine receptor Ab); Enbrel® (etanercept); Eprex® (Epoetin alfa); Erbitux® (Cetuximab); evolocumab; Genotropin® (Somatropin); Herceptin® (Trastuzumab); Humatrope® (somatropin [rDNA origin] for injection); Humira® (Adalimumab); Infergen® (Interferon Alfacon-1); Natrecor® (nesiritide); Kineret® (Anakinra), Leukine® (Sargamostim); LymphoCide® (Epratuzumab); Benlysta™ (Belimumab); Metalyse® (Tenecteplase); Mircera® (methoxy polyethylene glycol-epoetin beta); Mylotarg® (Gemtuzumab ozogamicin); Raptiva® (efalizumab); Cimzia® (certolizumab pegol); Soliris™ (Eculizumab); Pexelizumab (Anti-05 Complement); MEDI-524 (Numax®); Lucentis® (Ranibizumab); Edrecolomab (Panoree); Trabio® (lerdelimumab); TheraCim hR3 (Nimotuzumab); Omnitarg (Pertuzumab, 2C4); Osidem® (IDM-I); OvaRex® (B43.13); Nuvion® (visilizumab); Cantuzumab mertansine (huC242-DMI); NeoRecormon® (Epoetin beta); Neumega® (Oprelvekin); Neulasta® (Pegylated filgastrim, pegylated G-CSF, pegylated hu-Met-G-CSF); Neupogen® (Filgrastim); Orthoclone OKT3® (Muromonab-CD3), Procrit® (Epoetin alfa); Remicade® (Infliximab), Reopro® (Abciximab), Actemra® (anti-IL6 Receptor Ab), Avastin® (Bevacizumab), HuMax-CD4 (zanolimumab), Rituxan® (Rituximab); Tarceva® (Erlotinib); Roferon-A®-(Interferon alfa-2a); Simulect® (Basiliximab); Stelara™ (Ustekinumab); Prexige® (lumiracoxib); Synagis® (Palivizumab); 14667-CHO (anti-IL15 antibody, see U.S. Pat. No. 7,153,507), Tysabri® (Natalizumab); Valortim® (MDX-1303, anti-B. anthracis Protective Antigen Ab); ABthrax™; Vectibix® (Panitumumab); Xolair® (Omalizumab), ETI211 (anti-MRSA Ab), IL-I Trap (the Fc portion of human IgGI and the extracellular domains of both IL-I receptor components (the Type I receptor and receptor accessory protein)), VEGF Trap (Ig domains of VEGFR1 fused to IgGI Fc), Zenapax® (Daclizumab); Zenapax® (Daclizumab), Zevalin® (Ibritumomab tiuxetan), Zetia (ezetimibe), Atacicept (TACI-Ig), anti-α4β7 Ab (vedolizumab); galiximab (anti-CD80 monoclonal antibody), anti-CD23 Ab (lumiliximab); BR2-Fc (huBR3/huFc fusion protein, soluble BAFF antagonist); Simponi™ (Golimumab); Mapatumumab (human anti-TRAIL Receptor-1 Ab); Ocrelizumab (anti-CD20 human Ab); HuMax-EGFR (zalutumumab); M200 (Volociximab, anti-α5β1 integrin Ab); MDX-010 (Ipilimumab, anti-CTLA-4 Ab and VEGFR-I (IMC-18F1); anti-BR3 Ab; anti-C. difficile Toxin A and Toxin B C Abs MDX-066 (CDA-I) and MDX-1388); anti-CD22 dsFv-PE38 conjugates (CAT-3888 and CAT-8015); anti-CD25 Ab (HuMax-TAC); anti-TSLP antibodies; anti-TSLP receptor antibody (see U.S. Pat. No. 8,101,182); anti-TSLP antibody designated as A5 (see U.S. Pat. No. 7,982,016); (see anti-CD3 Ab (NI-0401); Adecatumumab (MT201, anti-EpCAM-CD326 Ab); MDX-060, SGN-30, SGN-35 (anti-CD30 Abs); MDX-1333 (anti-IFNAR); HuMax CD38 (anti-CD38 Ab); anti-CD40L Ab; anti-Cripto Ab; anti-CTGF Idiopathic Pulmonary Fibrosis Phase I Fibrogen (FG-3019); anti-CTLA4 Ab; anti-eotaxinl Ab (CAT-213); anti-FGF8 Ab; anti-ganglioside GD2 Ab; anti-sclerostin antibodies (see, U.S. Pat. No. 8,715,663 or 7,592,429) anti-sclerostin antibody designated as Ab-5 (see U.S. Pat. No. 8,715,663 or 7,592,429); anti-ganglioside GM2 Ab; anti-GDF-8 human Ab (MYO-029); anti-GM-CSF Receptor Ab (CAM-3001); anti-HepC Ab (HuMax HepC); MEDI-545, MDX-1103 (anti-IFNα Ab); anti-IGFIR Ab; anti-IGF-IR Ab (HuMax-Inflam); anti-IL12/IL23p40 Ab (Briakinumab); anti-IL-23p19 Ab (LY2525623); anti-IL13 Ab (CAT-354); anti-IL-17 Ab (AIN457); anti-IL2Ra Ab (HuMax-TAC); anti-IL5 Receptor Ab; anti-integrin receptors Ab (MDX-018, CNTO 95); anti-IPIO Ulcerative Colitis Ab (MDX-1100); anti-LLY antibody; BMS-66513; anti-Mannose Receptor/hCGβ Ab (MDX-1307); anti-mesothelin dsFv-PE38 conjugate (CAT-5001); anti-PDIAb (MDX-1 106 (ONO-4538)); anti-PDGFRα antibody (IMC-3G3); anti-TGFβ Ab (GC-1008); anti-TRAIL Receptor-2 human Ab (HGS-ETR2); anti-TWEAK Ab; anti-VEGFR/Flt-1 Ab; anti-ZP3 Ab (HuMax-ZP3); NVS Antibody #1; NVS Antibody #2; and an amyloid-beta monoclonal antibody comprising sequences, SEQ ID NO:8 and SEQ ID NO:6 (see U.S. Pat. No. 7,906,625).

Examples of antibodies suitable for the disclosed methods include the antibodies shown in Table 1. Other examples of suitable antibodies include infliximab, bevacizumab, ranibizumab, cetuximab, ranibizumab, palivizumab, abagovomab, abciximab, actoxumab, adalimumab, afelimomab, afutuzumab, alacizumab, alacizumab pegol, a1d518, alemtuzumab, alirocumab, alemtuzumab, altumomab, amatuximab, anatumomab mafenatox, anrukinzumab, apolizumab, arcitumomab, aselizumab, altinumab, atlizumab, atorolimiumab, tocilizumab, bapineuzumab, basiliximab, bavituximab, bectumomab, belimumab, benralizumab, bertilimumab, besilesomab, bevacizumab, bezlotoxumab, biciromab, bivatuzumab, bivatuzumab mertansine, blinatumomab, blosozumab, brentuximab vedotin, briakinumab, brodalumab, canakinumab, cantuzumab mertansine, cantuzumab mertansine, caplacizumab, capromab pendetide, carlumab, catumaxomab, cc49, cedelizumab, certolizumab pegol, cetuximab, citatuzumab bogatox, cixutumumab, clazakizumab, clenoliximab, clivatuzumab tetraxetan, conatumumab, crenezumab, cr6261, dacetuzumab, daclizumab, dalotuzumab, daratumumab, demcizumab, denosumab, detumomab, dorlimomab aritox, drozitumab, duligotumab, dupilumab, ecromeximab, eculizumab, edobacomab, edrecolomab, efalizumab, efungumab, elotuzumab, elsilimomab, enavatuzumab, enlimomab pegol, enokizumab, enokizumab, enoticumab, enoticumab, ensituximab, epitumomab cituxetan, epratuzumab, erlizumab, ertumaxomab, etaracizumab, etrolizumab, exbivirumab, exbivirumab, fanolesomab, faralimomab, farletuzumab, fasinumab, fbta05, felvizumab, fezakinumab, ficlatuzumab, figitumumab, flanvotumab, fontolizumab, foralumab, foravirumab, fresolimumab, fulranumab, futuximab, galiximab, ganitumab, gantenerumab, gavilimomab, gemtuzumab ozogamicin, gevokizumab, girentuximab, glembatumumab vedotin, golimumab, gomiliximab, gs6624, ibalizumab, ibritumomab tiuxetan, icrucumab, igovomab, imciromab, imgatuzumab, inclacumab, indatuximab ravtansine, infliximab, intetumumab, inolimomab, inotuzumab ozogamicin, ipilimumab, iratumumab, itolizumab, ixekizumab, keliximab, labetuzumab, lebrikizumab, lemalesomab, lerdelimumab, lexatumumab, libivirumab, ligelizumab, lintuzumab, lirilumab, lorvotuzumab mertansine, lucatumumab, lumiliximab, mapatumumab, maslimomab, mavrilimumab, matuzumab, mepolizumab, metelimumab, milatuzumab, minretumomab, mitumomab, mogamulizumab, morolimumab, motavizumab, moxetumomab pasudotox, muromonab-cd3, nacolomab tafenatox, namilumab, naptumomab estafenatox, narnatumab, natalizumab, nebacumab, necitumumab, nerelimomab, nesvacumab, nimotuzumab, nivolumab, nofetumomab merpentan, ocaratuzumab, ocrelizumab, odulimomab, ofatumumab, olaratumab, olokizumab, omalizumab, onartuzumab, oportuzumab monatox, oregovomab, orticumab, otelixizumab, oxelumab, ozanezumab, ozoralizumab, pagibaximab, palivizumab, panitumumab, panobacumab, parsatuzumab, pascolizumab, pateclizumab, patritumab, pemtumomab, perakizumab, pertuzumab, pexelizumab, pidilizumab, pintumomab, placulumab, ponezumab, priliximab, pritumumab, PRO 140, quilizumab, racotumomab, radretumab, rafivirumab, ramucirumab, ranibizumab, raxibacumab, regavirumab, reslizumab, rilotumumab, rituximab, robatumumab, roledumab, romosozumab, rontalizumab, rovelizumab, ruplizumab, samalizumab, sarilumab, satumomab pendetide, secukinumab, sevirumab, sibrotuzumab, sifalimumab, siltuximab, simtuzumab, siplizumab, sirukumab, solanezumab, solitomab, sonepcizumab, sontuzumab, stamulumab, sulesomab, suvizumab, tabalumab, tacatuzumab tetraxetan, tadocizumab, talizumab, tanezumab, taplitumomab paptox, tefibazumab, telimomab aritox, tenatumomab, tefibazumab, telimomab aritox, tenatumomab, teneliximab, teplizumab, teprotumumab, TGN1412, tremelimumab, ticilimumab, tildrakizumab, tigatuzumab, TNX-650, tocilizumab, toralizumab, tositumomab, tralokinumab, trastuzumab, TRBS07, tregalizumab, tremelimumab, tucotuzumab celmoleukin, tuvirumab, ublituximab, urelumab, urtoxazumab, ustekinumab, vapaliximab, vatelizumab, vedolizumab, veltuzumab, vepalimomab, vesencumab, visilizumab, volociximab, vorsetuzumab mafodotin, votumumab, zalutumumab, zanolimumab, zatuximab, ziralimumab and zolimomab aritox. Most preferred antibodies for use in the disclosed formulations and methods are adalimumab, bevacizumab, blinatumomab, cetuximab, conatumumab, denosumab, eculizumab, erenumab, evolocumab, infliximab, natalizumab, panitumumab, rilotumumab, rituximab, romosozumab, and trastuzumab, and antibodies selected from Table 1.

TABLE 1 Examples of therapeutic antibodies Target (informal Conc. Viscosity HC Type (including LC LC SEQ HC SEQ name) (mg/ml) (cP) allotypes) Type Pl ID NO ID NO anti-amyloid 142.2 5.0 IgG1 (f) (R; EM) Kappa 9.0 1 2 GMCSF (247) 139.7 5.6 IgG2 Kappa 8.7 3 4 CGRPR 136.6 6.3 IgG2 Lambda 8.6 5 6 RANKL 152.7 6.6 IgG2 Kappa 8.6 7 8 Sclerostin 145.0 6.7 IgG2 Kappa 6.6 9 10 (27H6) IL-1R1 153.9 6.7 IgG2 Kappa 7.4 11 12 Myostatin 141.0 6.8 IgG1 (z) (K; EM) Kappa 8.7 13 14 B7RP1 137.5 7.7 IgG2 Kappa 7.7 15 16 Amyloid 140.6 8.2 IgG1 (za) (K; DL) Kappa 8.7 17 18 GMCSF (3.112) 156.0 8.2 IgG2 Kappa 8.8 19 20 CGRP (32H7) 159.5 8.3 IgG2 Kappa 8.7 21 22 CGRP (3B6.2) 161.1 8.4 IgG2 Lambda 8.6 23 24 PCSK9 (8A3.1) 150.0 9.1 IgG2 Kappa 6.7 25 26 PCSK9 (492) 150.0 9.2 IgG2 Kappa 6.9 27 28 CGRP 155.2 9.6 IgG2 Lambda 8.8 29 30 Hepcidin 147.1 9.9 IgG2 Lambda 7.3 31 32 TNFR p55 ) 157.0 10.0 IgG2 Kappa 8.2 33 34 OX40L 144.5 10.0 IgG2 Kappa 8.7 35 36 HGF 155.8 10.6 IgG2 Kappa 8.1 37 38 GMCSF 162.5 11.0 IgG2 Kappa 8.1 39 40 Glucagon R 146.0 12.1 IgG2 Kappa 8.4 41 42 GMCSF (4.381) 144.5 12.1 IgG2 Kappa 8.4 43 44 Sclerostin (13F3) 155.0 12.1 IgG2 Kappa 7.8 45 46 CD-22 143.7 12.2 IgG1 (f) (R; EM) Kappa 8.8 47 48 INFgR 154.2 12.2 IgG1 (za) (K; DL) Kappa 8.8 49 50 Ang2 151.5 12.4 IgG2 Kappa 7.4 51 52 TRAILR2 158.3 12.5 IgG1 (f) (R; EM) Kappa 8.7 53 54 EGFR 141.7 14.0 IgG2 Kappa 6.8 55 56 IL-4R 145.8 15.2 IgG2 Kappa 8.6 57 58 IL-15 149.0 16.3 IgG1 (f) (R; EM) Kappa 8.8 59 60 IGF1R 159.2 17.3 IgG1 (za) (K; DL) Kappa 8.6 61 62 IL-17R 150.9 19.1 IgG2 Kappa 8.6 63 64 Dkk1 (6.37.5) 159.4 19.6 IgG2 Kappa 8.2 65 66 Sclerostin 134.8 20.9 IgG2 Kappa 7.4 67 68 TSLP 134.2 21.4 IgG2 Lambda 7.2 69 70 Dkk1 (11H10) 145.3 22.5 IgG2 Kappa 8.2 71 72 PCSK9 145.2 22.8 IgG2 Lambda 8.1 73 74 GIPR (2G10.006) 150.0 23.0 IgG1 (z) (K; EM) Kappa 8.1 75 76 Activin 133.9 29.4 IgG2 Lambda 7.0 77 78 Sclerostin (2B8) 150.0 30.0 IgG2 Lambda 6.7 79 80 Sclerostin 141.4 30.4 IgG2 Kappa 6.8 81 82 c-fms 146.9 32.1 IgG2 Kappa 6.6 83 84 α4β7 154.9 32.7 IgG2 Kappa 6.5 85 86 * An exemplary concentration suitable for patient administration; {circumflex over ( )}HC—antibody heavy chain; LC—antibody light chain.

In some embodiments, the therapeutic polypeptide is a BiTE® molecule. BiTE® molecules are engineered bispecific monoclonal antibodies which direct the cytotoxic activity of T cells against cancer cells. They are the fusion of two single-chain variable fragments (scFvs) of different antibodies, or amino acid sequences from four different genes, on a single peptide chain of about 55 kilodaltons. One of the scFvs binds to T cells via the CD3 receptor, and the other to a tumor cell via a tumor specific molecule. Blinatumomab (BLINCYTO®) is an example of a BiTE® molecule, specific for CD19. BiTE® molecules that are modified, such as those modified to extend their half-lives, can also be used in the disclosed methods.

EXAMPLES Example 1—Overview

All of the instruments used in these studies include a SoloVPE connected to an Agilent Cary 60 ultraviolet (UV) spectrophotometer system (Agilent Technologies; Santa Clara, Calif.). To make a concentration determination, the SoloVPE automatically adjusts the optical path length from 0.005 mm to 15 mm as dependent on absorbance of the sample. For each sample, an absorbance versus path length linear regression plot is generated using a maximum of 10 different path lengths (5 points are minimally required). The sample acceptance criteria are based on the regression line of this sample analysis plot, which R² must be 0.999 for the SoloVPE to provide a valid result. Based on the slope measuring capability and path length range of the SoloVPE system, the manufacturer's claimed protein sample concentration determination capability range is 0.01 to 300 mg/mL (bovine serum albumin) without the need for dilutions (U.S. Pat. No. 7,808,641 Example 4).

The purpose of this study was to establish the scientific basis for the system suitability criteria, assay and sample acceptance criteria using the PBD as a system suitability standard with version 3 of the SoloVPE software.

Example 2—Materials and Methods, Experiments, and Data Analysis

Preparation of 0.12% PBD (from 0.12% to 0.5% can be Used and Optimized by One of Skill in the Art)

1. Add 120±5 mg of PBD to an appropriately sized beaker.

2. Add 99 mL of HPLC grade water to the beaker.

3. Add 1 mL of methanol to the beaker.

4. Mix well with a stir bar.

5. Transfer to an HPLC bottle.

6. Store at room temperature in the dark.

PBD UV/Visible spectrum

The UV/Visible spectrum of the PBD is shown in FIG. 1. Three wavelengths are highlighted in the figure, 280 nm, 310 nm, and 639 nm. The PBD is certified for accuracy at 280 nm and 310 nm for slopes (absorbance values) and is shipped with a certificate of analysis (CoA) as traceable through the National Institute of Standards and Technology (NIST). The slope (absorbance) at 639 nm is not certified by the PBD manufacturer or by NIST. The certified PBD readings at 280 nm and 310 nm provide the basis for the assessment of accuracy for the instrument and were evaluated prior to each assay.

In the Examples, when an “instrument” is cited, the reference includes the Cary 60 spectrophotometer connected to a SoloVPE instrument. The proteins were monoclonal antibodies (mAbs).

Table 2.1 shows the proteins that were analyzed and their concentration.

TABLE 2.1 Samples analyzed Protein Certified Value* mAb1 135.8 mg/mL mAb2 48.7 mg/mL mAb2 9.7 mg/mL PBD (C Technologies, Inc.) 0.5825 Slope (abs/mm) at 280 nm) 1.2849 Slope (abs/mm) at 310 nm)

Execution of Experiments

Each test sequence or run consisted of 36 protein determinations at three different concentrations (12 readings at each concentration level: 9.7 (mAb2), 48.7 (mAb2), and 135.8 mg/mL (mAb1)), bracketed (beginning and end of sample testing) with triplicate readings of the PBD at both 280 nm and 310 nm to assess system suitability and establish assay acceptance criteria. The testing strategy was designed to mimic routine testing and evaluate the use of the system suitability with PBD.

The testing sequence used for assessing system suitability:

3 standard readings of PBD (280 nm) 3 standard readings of PBD (310 nm) 12 low protein concentration runs (9.7 mg/mL) 12 mid protein concentration runs (48.7 mg/mL) 12 high protein concentration runs (135.8 mg/mL) 3 standard readings of PBD (280 nm) 3 standard readings of PBD (310 nm) Overall, 14 data sets were obtained.

The strategy of evaluating the PBD readings at two wavelengths were used to cover the broad range of protein concentrations required of the instrument. Higher protein concentrations (such as was tested in the Examples, 135.8 mg/mL) required the lowest range of path lengths from 5 μm to 50 μm. The PBD readings at 310 nm evaluated instrument performance at path lengths less than 50 μm. For the mid-range concentration determination (such as the 48.7 mg/mL (mAb2) sample), the instrument used the path lengths that ranged from 20 μm to 65 μm. To cover the remaining range of protein concentrations (i.e. 48.7 mg/mL tested in these examples), the readings at 280 nm assessed the instrument performance at path lengths greater than 50 μm.

All instruments used were running version 3 of the Quick Slope Software from C Technologies, Inc. Two instrument modes were used and were required for testing a sample with the required system suitability criteria:

1) Quick Slope Mode (Quick-M): Threshold path length search performed for Target Absorbance, Section data collected using adaptive algorithm based upon desired number of data points.

2) Fixed Slope Mode (Fixed-M): No initial path length search. Data is collected based upon user specified starting path length, path length step size and number of data points to be collected.

A PBD-specific Fixed Slope Mode subroutine was created and used to obtain the data at the 310 nm wavelength. This subroutine forces the instrument to use the 5 μm to 50 μm path lengths to assess instrument performance for higher protein concentrations. Measurements of a sample set absorbance by SoloVPE were performed by three analysts to observe any associated difference in the results that may occur. Determinations of the protein concentration and PBD readings were analyzed by SoloVPE spectrophotometer at the time of measurement.

Data Analysis

All statistical analyses in this report were performed using SAS® 9.4 (TS1M3; Cary, N.C.). Four statistical analyses were performed in this study:

1) To compare the distribution of the PBD readings across the 10 different runs, a box plot was generated for 280 nm and 310 nm. A box plot provides a quick visual representation of the center of the data and its spread, making comparisons across runs easier.

2) To assess the impact of the worst-case, test-retest error and the ±4% and ±5% specifications normal density curves were generated for the 280 nm and the 380 nm of the PBD. The curves depict the distribution of the measure given a particular test-retest error. The worst-case test-retest error was define as the upper 95% confidence bound on the test-retest.

3) To evaluate the impact of the PBD input on the SoloVPE readings, bivariate normal contour plots were generated taking into account the correlation between the PBD and SoloVPE measurements. The contours were compared against the specifications to assess the misclassification rates.

4) Bootstrap sampling using random sampling with replacement were used to evaluate the distribution of the coefficient of variation, and its proximity to the upper bound. The determinations of the coefficient of variation (% RSD) for the protein samples were below the 5% target limit.

Further Information: Readings

The tables shown in FIGS. 2 and 3 present the raw data for the PBD readings and the protein determinations, respectively. One hundred twenty of the 168 readings per protein concentration level and the 60 of the 84 PBD readings at each wavelength (280 nm and 310 nm) were used to demonstrate the system suitability, assay acceptance and sample acceptance criteria. These data were from three instruments and were used for showing the system suitability criteria as the readings were within ±5% of the certified absorbance value and met 5% RSD of triplicate readings. The invalid readings in this data set were 0 reading out of the 60 readings (0 run of 10 runs invalid) of the PBD at 280 nm or 310 nm.

A fourth instrument used in the study was known to be a “sub-optimally” functioning and was used to demonstrate the utility of the developed system suitability using the PBD. The use of this instrument provided valuable insight to the type of errors that may occur. All data from this instrument were not considered in the determination of the working system suitability criteria, but instead were used to show how the PBD-based criteria could reveal a poorly functioning instrument.

This instrument performed poorly on two of the three testing days, and the third data set was discounted due to the instrument instability despite passing criteria for that day. The shaded data of the tables in FIGS. 2 and 3 are test runs that failed the working system suitability criteria. These determinations and readings were not considered valid so excluded from consideration in the system suitability criteria determinations.

In addition, Run 12 (FIG. 2) using the 1134 instrument, a single reading of the triplicate set of the PBD readings at 310 nm caused the system suitability to fail and the data from this run was excluded from the system suitability determination. This failure was not the fault of the PBD usage, but demonstrated that the PBD system suitability realized an anomalous single reading by the instrument as the subsequent readings in that triplicate set were within expected values. If this was included in the invalids, then the invalids would be 1 out of 11 runs because of a single anomalous reading or 1 reading out of 72 readings of the PBD at 310 nm and 0 reading of 72 readings at 280 nm.

Example 3—Evaluation of PBD as System Suitability Standard

This section discusses the use of the PBD as the system suitability standard in terms of accuracy and precision of the readings on four instruments. Accuracy was assessed by plotting the individual readings in relation to the certified value as referenced on the CoA. The differences of the reading from the certified values were plotted as shown in FIG. 4. The box plots show all boundary lines at a 5% difference from the PBD CoA target value is acceptable. A similar plot of the 4% difference showed data points residing on the 4% boundary line, thereby indicating that the criteria for % difference from target for the PBD reading should be 5%.

Two observations can be made regarding these data plots. First, in the initial days of the study (R01-R04), a trend of increasing absorbance readings (by +3% over the 4 days) was observed at the 310 nm wavelength. The trend approaches the upper limits of the 4% boundary line, but well within the 5% boundary line. The readings (i.e. 6 PBD readings each day) were obtained by the same analyst using the same sample lot on the same instrument. This suggests that this trend is not random and shows the inter-day variability of the instrument.

Next, there were inconsistent readings on day 7 (R07) and day 9 (R09) at 280 nm (FIG. 4) where single data points were outside of the boxed range. Data obtained using the 310 nm wavelength (FIG. 4) showed that while the readings were more centered on the target, the deviations from the mean were more pronounced (days 6, 7, and 9 (R06, R07, and R09)).

While the unpredictability of these readings by the instrument are prime examples of variations from the target or from the certified values, these deviations remain within the 5% range as denoted by the horizontal dashed lines.

In order to reliably set criteria on the accuracy of the instrument using the PBD, a Test-Retest was calculated. Test-Retest is defined as a measure of repeatability obtained by administering the same test multiple times over a period of time to the same group of instruments and analysts. Table 3.1 lists the Test-Retest results (obtained from measured PBD readings) for both wavelengths and the 95% Upper Confidence Bound or the “worst-case” (calculated from the CoA value).

TABLE 3.1 Test-Retest Results 95% Upper Confidence Bound Sample Test-Retest “Worst-case” PBD at 280 nm 0.0062 0.0076 PBD at 310 nm 0.0165 0.0202

With the Test-Retest and the worst-case values established from the raw data set (Table 3.1), the criteria for instrument accuracy can be calculated. The proposed 4% or 5% of target variability of the instrument was considered 3 standard deviations from the true value. For a criterion to pass, one standard deviation of the certified value or should be calculated (4% or 5% of the certified value divided by three). The quotient of these calculations represents the worst-case. If the proposed criterion (4% or 5% of target) exceeds the worst-case, then the probability of failure is likely.

FIG. 5 shows the normal distribution of the readings using a single standard deviation based on a 4% of target curve (middle line, overlapping parts with the dashed curve), a 5% of target curve (lowest peak curve), and the worst-case (dashed line). The x-axis shows the deviation of readings from target with the center line of the graph as the target, while the y-axis displays the probability of the reading being on target. The 4% and 5% curves were used to evaluate the proposed criteria and the acceptability of either was assessed from the worst-case curve as derived from the CoA value. In order to evaluate if 4% or 5% of target criteria was best-suited, the values of the PBD readings must be below the worst-case upper bound.

The density plot of the 4% target values at 280 nm (FIG. 5) shows that the worst-case is within a single standard deviation of the CoA value (middle line curve is below the red-dashed curve). Therefore, the system suitability at 4% of target would pass at 280 nm. However, at 310 nm (FIG. 6), the 4% target curve (the curve with the highest peak) is significantly above of the worst-case, and therefore, the system suitability criterion would fail if set at 4% from target.

Alternatively, with the criterion set at 5% of target, a quotient of 0.029125 (5% of 0.5825), then one standard deviation is found by dividing the standard deviation by 3 to equals 0.009708.

This value is the worst-case for a PBD reading. The Test-retest at 280 nm is 0.0062 which is less than the worst-case (0.0076), so a 5% target is acceptable.

Performing similar calculations for the PBD at 310 nm, the CoA target is 1.2849, so 5% of target is 0.064245. One standard deviation of the 5% of target is 0.021415. A comparison of the standard deviation with the Worst-case value of the Test-retest (0.0202) at 310 nm proves that the 5% target is acceptable.

While the Test-Retest Analysis considered only the variation in instrument accuracy, the variability associated with the certified PBD absorbance should also be considered. As noted on the CoA, the error associated with the PBD certified value reading at each wavelength is ±5%. An assessment of this error can be made through the relationship between the measured and true values can be described using a bivariate normal distribution as based on the equation below:

Measured Value=(PBD Target+PBD Error)+Solo VPE Measurement Error  (Eq. 1)

FIGS. 7 and 8 show normal bivariate contours of the data set in consideration of the variation or errors associated with the instrument and the reliability of the certified value of the PBD reading. All PBD readings outside the CoA range (vertical lines) are rejected. Likewise, instrument readings outside of the horizontal lines are rejected. Taken together, these boundaries set the acceptable window for SoloVPE and PBD Sample and Test acceptance as based on overall variability in the Measured Value. The shaded contours as shown in the figures below are evaluated for containment within the acceptance window (i.e., center box). As shown in FIGS. 7 and 8, the PBD readings at 280 nm and 310 nm overlap the boundaries of the ±4% target specification. The PBD readings at both wavelengths allow a ±5% target specification as all of the contours are within the center box. Therefore, as based on the bivariate statistical analysis, accounting for the variation for the SoloVPE instrument and the variability of the PBD results, a ±5% difference criteria are supported.

Example 4—Instrument Performance: Correlation of PBD Readings with Protein Determinations

This section discusses the utility of the PBD readings to predict instrument performance with regards to protein concentration determinations. Overall, the system suitability criteria were able to discern poor instrument performance. As shown by the % RSD in Table 3.1, there were no exceptional variations in the PBD readings at the 280 nm wavelength for 3 instruments (1134, 1174 and 1711) as evidenced by the % RSD at levels below 2.2%. PBD readings at this wavelength were also within the 5% criteria as compared to the certified value (FIG. 7). Moreover, all and the subsequent protein determinations at the low and mid concentration levels were within the ±5% range from the certified value with exception of the poorly performing instrument (FIG. 9). For the high concentration protein samples (e.g., 135.8 mg/mL; mAb1), the PBD readings at the 310 nm wavelength would be most applicable to use as a predictor of the instrument performance as based on path lengths assessed. A direct comparison plots are presented in FIG. 10.

The data points, highlighted by the circles in FIG. 10 spotlight the anomalous readings obtained with the poorly performing instrument. Individual readings from the tables in FIGS. 2 and 3 for the PBD readings at 310 nm and mAb1 determinations were compared graphically for identification of a patterns. Overall, the plot shows a similar pattern of PBD readings compared to protein determinations across all four instruments (1711, 1134, 1174, PP). This similarity indicated that the PBD was a good predictor of instrument performance. The PBD readings and the protein determinations were mostly within the 5% of target value (blue lines), but there were noticeable exceptions as discussed below.

The focus of Circle #1 is the 2 PBD readings from a test run at 310 nm. It was these data points that caused the % RSD to fail the 5% RSD criterion (10.5% RSD observed). It is noteworthy that these two readings occurred at the end bracket (FIG. 3), which suggested that the instrument was unstable throughout the test sequence. On the following day, the PP instrument provided low protein concentration determinations that were outside the ±5% range of the CoA value (blue and green diamonds) for mAb1 (Circle #2). These anomalous low results are discussed later in this section.

The data in Circles 3 and 4 clearly demonstrate the predictive utility of the PBD readings to the protein concentration determinations. Due to the large magnitude of the deviation from target at 310 nm, further investigation into the cause of the anomalous data was warranted. In summary though, the PBD based system suitability criteria was able to discern this poor instrument performance.

This investigation was centered on the readings taken the PP instrument. From the data shown in the table in FIG. 2, in contrast to the lower PBD readings at 310 nm, the readings for the PBD at 280 nm were significantly higher than the certified value. These observations could be explained through a shift to a longer wavelength by the monochromator of the Cary 60 spectrophotometer. The spectrum of the PBD shows that at 280 nm, the absorbance peak is still rising, however at 310 nm, there is a maxima. Moreover, a monochromator wavelength error would also explain the perceived lower protein concentration readings, as proteins have a maxima at 280 nm and the protein readings at longer wavelengths than 280 nm would deviate away from the maxima therefore decrease the absorbance. FIG. 11 presents graphically the spectra and shows the wavelength shift impact to absorbance for the PBD readings at 280 nm, 310 nm, and the mAb1 protein determination. If the Cary 60 shifted the wavelength then the extinction coefficient used by the SoloVPE would be incorrect for the shifted wavelength, thereby incorrectly calculating the concentration.

Because no investigation of either the SoloVPE or Cary 60 for this run was performed at the time of the measurement, the exact root cause of the anomalous readings cannot be assigned. However, the percent offset difference observed for the PBD readings and protein determinations in this test run can be compared to the average passing values from other instruments in the study. The differences can then be applied to all the measurements. For example, the average of the anomalous PBD readings at 280 nm in this run's data set was 0.7892 or 137.7% higher than the average of the passing results at 280 nm (0.5738, average of runs 1-6, 10-11, and 13-14 as listed in the table in FIG. 2). The absorbance from the fixed path length spectral data at 280 nm was 0.3029 AU. The observed absorbance reading, adjusted for the 137.7% difference gives an absorbance of 0.4150 AU, which when plotted on the spectral curve would correspond to a wavelength of 290.9 nm or a 10.8 nm higher than the nominal wavelength (FIG. 11). The same calculation was performed at the other wavelengths and protein samples.

These differences in readings indicate that the absorbance values may have been obtained with an incorrect wavelength of approximately 8.8 nm to 10.8 nm off from nominal. The consistency of the data for the PBD and protein samples indicate the monochromator of the Cary 60 could have been a contributor to the cause of the unusual data in this run. Agilent recommends that the instrument should be shut down on a monthly basis as Cary 60 spectrophotometer calibrates the wavelength on start-up. It should be noted that the instrument performed better the next day (FIG. 5). Overall, the system suitability criteria were able to discern this poor instrument performance.

Example 5—Determination of Sample Acceptance Criteria

This section examines the use of replicate readings instead of a single determination for protein concentration. An acceptance criterion for replicate reading using the fixed path length instruments was set at 5% RSD of duplicate and triplicate readings.

As discuss earlier, the data show that the unpredictability of the occurrence of an anomalous single reading can impact the validity of an entire data set. Three PBD readings failed the RSD criteria of 5% (Table in FIG. 2). In another test run, two of the three readings were higher than the certified value and caused the % RSD to be >5% (10.5% RSD), thereby failing the criteria. Similarly, in yet another test run, a single reading was recorded above the certified value that caused the % RSD criteria to fail (9.0% RSD). By requiring the use of the PBD at both wavelengths at the beginning and end of the sample run, the system suitability was able to discern instrument drift. If these anomalous readings were observed in a sample data set, the protein determinations would be invalid. In the event of a single anomalous reading thereby causing a failure, replicate sample testing would provide the investigator real time data (as meaning the other readings in the triplicate set) to assign the root cause as either sample related or to merely a random event of the instrument.

Example 5—Summary

In summary, an instrument accuracy criteria of ±5% from the PBD certificate of analysis value is established, based the data in this study using a statistical analysis of the data. Second, the working system suitability criteria used in this study and summarized in this report were able to discern a poorly functioning instrument. When a properly functioning instrument was used as for the 1711, 1134, and 1174 instruments, the invalid readings is essentially zero. The PBD based system suitability demonstrated its utility through providing evidence that an anomalous single reading by the instrument can impact data validity. For assay acceptance criteria, this limited pilot study showed that 36 individual protein readings could be made with consistent inter-sample results. Lastly, each protein sample should be tested in triplicate as based on the bootstrap analysis. Although this study used two mAbs, based on first principles, all proteins should behave similarly.

Example 6—Programming of SoloVPE

Quick Slope

Under the Quick Slope tool, select the parameters from Tables 6.1 and 6.2:

TABLE 6.1 Quick Slope Parameters Menu Item Selection (or Input) Quick Methods None Slope Mode Quick - M “. . .” See Table 6.2 Below Sample Vessel PV-OC0009-1 Wavelength (nm) 280.00 Ext. Coefficient User EC Value 1.00000 mL/(mg*cm) Baseline Correction Off Scatter Correction Off Reps Replicate (3)

TABLE 6.2 Quick Slope Configuration Menu Item Input Data points 10 Target Abs 1.00000 Search PL1 (mm) 0.005 Search PL2 (mm) 0.025 Search PL3 (mm) 0.050 Avg Time (s) 0.5000

Fixed Slope

Under the Quick Slope tool, select the parameters from Tables 6.3 and 6.4:

TABLE 6.3 Fixed Slope Parameters Menu Item Selection (or Input) Quick Methods None Slope Mode Fixed - M “. . .” See Table 6.4 Below Sample Vessel PV-OC0009-1 Fixed Slope Wavelength(s) (nm) 310.00 Ext. Coef User “. . .” EC Value: 1.00000 ml/(mg*cm) Baseline Correction Off Scatter Correction Off Reps Replicate (3)

TABLE 6.4 Fixed Slope Configuration Menu Item Input Datapoints 10 Start PL (mm) 0.050 Step PL (mm) 0.005 Avg Time (s) 0.5000

Screenshots for Fixed Slope Mode are shown in FIG. 13.

Example 7—Overview

System suitability, assay and sample acceptance criteria were re-evaluated for the determination of protein concentrations involving the variable path length instrument, SoloVPE in Examples 7 and 8. Intermediate precision data were obtained using AMG Blue (see below) for instrument variability. Data for the revision of these criteria were obtained using the SoloVPE at six instruments. AMG Blue is a buffered Patent Blue Dye solution (pH 6.8) at 0.15% (w/v) in 5% (v/v) glycerol water mixture. Analyses of this data revealed that 4% of fixed path length value at 280, 310, 510, and 615 nm were acceptable. The precision of the system suitability readings must have a relative standard deviation (RSD) percentage of 5% at all wavelengths. The ConfiRM® standard is not suited for the use as a system suitability standard as based on path lengths used and the step absorbance.

All the instruments used in this study included a SoloVPE connected to an Agilent Cary 60 ultraviolet (UV) spectrophotometer system. To make a concentration determination, the SoloVPE automatically adjusted the optical path length from 0.005 mm to 15 mm as dependent on absorbance of the sample. For each sample, an absorbance versus path length linear regression plot was generated using a maximum of 10 different path lengths (5 points were minimally required). The sample acceptance criteria were based on the regression line of this sample analysis plot, which R² must be 0.999 for the SoloVPE to provide a valid result. Based on the slope measuring capability and path length range of the SoloVPE system, the manufacturer's claimed protein sample concentration determination capability range is 0.01 to 300 mg/mL (bovine serum albumin) without the need for dilutions. As a result, the SoloVPE coupled with the Cary spectrophotometer was well suited for quality control and on the manufacturing floor to gain efficiency through improved speed of testing.

The purpose of this study was to establish the scientific basis for the use of AMG Blue as the system suitability standard, simplifying the system suitability procedure.

Example 8—Materials and Methods, Experiments, and Data Analysis

Preparation of the AMG Blue Dye

The UV/Visible spectrum of the AMG Blue dye is shown in FIG. 14. Four wavelengths are highlighted in the figure, 280 nm, 310 nm, 510 nm and 615 nm. The currently used dye solution, CHEM013 (PBD) is supplied by C Technologies, Inc. for the instrument qualification but in a lower concentration and with different formulation.

To prepare the AMG Blue dye (0.15% Patent Blue VF in 1×PBS, 5% Glycerol Buffer), the following procedure was followed:

1. Add 10 mL of 10× Dulbecco's phosphate buffered saline* (DPBS; without CaCl₂ without MgCl₂; Gibco, p/n 14200-075; Thermo Fisher Scientific; Waltham, Mass.) to a 100 mL graduated cylinder or volumetric flask.

2. Add 10 mL of sterile 50% glycerol (Teknova, p/n G1799; Hollister, Calif.) to the graduated cylinder or flask.

3. Bring the volume in the graduated cylinder or flask to 100 mL with purified water.

4. Cap or seal the cylinder/flask and invert several times to thoroughly mix the solution.

5. In a separate beaker, weigh 150±2 mg of Patent Blue VF (aka Acid Blue 1, Sulfan Blue, formula (Hill notation) C₂₂H₃₁N₂NaO₆S₂; CAS Number 129-17-9; Sigma, p/n 198218; Millipore Sigma, St. Louis, Mo.).

6. Slowly add the DPBS/glycerol solution to the beaker, taking care to not cause splashing.

7. Add a magnetic stir bar to the beaker and stir for 10 minutes.

8. Check pH to be 7.0±0.2

9. Transfer to a storage bottle.

10. Store at room temperature in the dark.

*In addition to DPBS, any buffer system that buffers at a pH of 6.8-9.0 is suitable. Exemplary buffers are shown in Table A.

TABLE A Exemplary buffers Useful Buffer pH range MES 5.5-6.7 Bis-Tris 5.8-7.2 ADA 6.0-7.2 ACES 6.1-7.5 PIPES 6.1-7.5 MOPSO 6.2-7.6 Bis-Tris Propane  63-9.5 BES 6.4-7.8 MOPS 6.5-7.9 TES 6.8-8.2 HEPES 6.8-8.2 DIPSO 7.0-8.2 MOBS 6.9-8.3 TAPSO 7.0-8.2 Tris or Trizma ® 7.0-9.0 HEPPSO 7.1-8.5 POPSO 7.2-8.5 TEA 7.3-8.3 EPPS 7.3-8.7 Tricine 7.4-8.8 Gly-Gly 7.5-8.9 Bicine 7.6-9.0 HEPBS 7.6-9.0 TAPS 7.7-9.1 AMPD 7.8-9.7 TABS 8.2-9.6 AMPSO 8.3-9.7 CHES  8.6-10.0 CAPSO  8.9-10.3 AMP  9.0-10.5 CAPS  9.7-11.1 CABS 10.0-11.4 Phosphate (potassium 5.7-8.0 phosphate monobasic anhydrous: sodium phosphate dibasic heptahydrate) Citric acid 2.6-7.6 monohydrate: Na2HPO4 Na2HPO4: NaH2PO4 5.8-8.0 Imidazole-HCl 6.2-7.8

Experimental Design

Intermediate precision study examined the reproducibility of an AMG Blue across multiple instruments at different locations.

Six instruments were used in this study. All instruments used were upgraded by the manufacturer to version 3 of the Quick Slope Software from C Technologies, Inc. The instrument mode was Multi-Mode. The instrument's software possesses three modes:

1) Quick Slope Mode (Quick-M): Threshold path length search performed for Target Absorbance, section data collected using adaptive algorithm based upon desired number of data points.

2) Multi-Mode (Multi-M): Multiple wavelengths are tested using the Quick Slope Mode algorithm.

3) Fixed Slope Mode (Fixed-M): No initial path length search. Data are collected based upon user specified starting path length, path length step size and number of data points to be collected.

For this study, the following settings were used:

Multi-Mode at Wavelengths: 280.00, 310.00, 510.00, 615.00

Averaging time: 0.5 sec; 12 runs per instrument (2 sets of 6 replicates)

Blue dye-specific Fixed Slope Mode subroutine was created and used to obtain the data at the 310 nm wavelength. This subroutine forces the instrument to use the 5 μm to 50 μm path lengths to assess instrument performance for high protein concentrations and is described. This subroutine requires version 3 software for the system suitability runs.

Execution of Experiments

The experiments were executed using an acceptance criterion for replicate reading using the fixed path length instruments, set at 5% RSD of duplicate and triplicate readings. This RSD criterion was used and evaluated in this study.

Each test sequence consisted of 12 AMG Blue determinations per instrument at both 280, 310, 510, and 615 nm to assess system suitability criteria. The testing strategy was designed to reduce overall operator time and effort. Eight data sets were obtained. The testing strategy was designed to evaluate the inter-instrument differences with the AMG Blue Solution. A critical attribute to the success was the instrument' absorbance at 50 μm path length being consistently at or above 1 absorbance unit (AU). The current PBD solution is not capable of reading 1 AU at 50 μm, but instead the algorithm moves the path length to a reading of 1 AU. The AMG Blue solution when measured by the SoloVPE consistently provides 1 AU at 50 μm.

The strategy of evaluating the AMG Blue dye readings at multiple wavelengths was employed to cover the broad range of protein concentrations required of the instrument. Higher protein concentrations (i.e. >45 mg/mL monoclonal antibody (mAb)) required the lowest range of path lengths from 5 μm to 50 μm. The Blue dye readings at 615 nm evaluated instrument performance at path lengths less than 50 μm. To cover the remaining range of protein concentrations (i.e. 48 mg/mL), the readings at 510 nm assessed the instrument performance at path lengths used for very low concentration samples 50 μm. Determinations at 280 nm and 310 nm were added for the comparison between previous runs. Protein concentrations are typically determined at 280 nm.

The AMG Blue dye enabled a procedure which uses the Multi-Mode which is the Quick Slope mode at multiple wavelengths. No specified path lengths were required prior to the determination as the instrument's algorithm determined the best testing strategy (i.e. threshold path length and step absorbance). Measurements of absorbance by SoloVPE were performed on six instruments to observe any associated difference in the results that may occur. Calculations of the AMG Blue dye readings for slope and RSD % were performed by SoloVPE software at the time of measurement.

Data Analysis

All statistical analyses were performed using Microsoft® Excel software. Intermediate precision studies were carried out using AMG Blue dye.

This section discusses the use of the AMG Blue dye as the system suitability standard in terms of accuracy and precision of the readings on six instruments. As shown in Table 8.1, data from six instruments were within 5% of the fixed path length and met 5% RSD of triplicate readings as based on the % RSD criteria of replicate readings. Table 8.2 presents the raw data for the AMG Blue dye readings and the protein determinations, respectively. In this study, 95 readings per wavelength were used to demonstrate the system suitability criteria. Accuracy was assessed by plotting the individual readings in relation to fixed path length instrument (Cary 60). These data were available in Microsoft® Excel format.

TABLE 8.1 Summary of Intermediate Precision of AMG Blue Dye for System Suitability Evaluation Wavelength 280 nm 310 nm 510 nm 615 nm Total Average 1.4172 3.9080 0.4805 13.3339 Total St Dev 0.03 0.05 0.01 0.24 Total % RSD 2.21 1.30 1.63 1.81 Total % Diff from FPL 3.24 0.24 1.29 0.80

In previous experiments, the absorbance at 639 nm was used as the high concentration model. The goal was to determine the slope (abs/mm) at 639 nm and compare to the Fixed Path length instrument readings. Due to instrument detector limitations and Beer's Law deviations, there was no match in the slope determinations between the fixed path length and the SoloVPE determinations. The likely cause of the poor correlation was likely due to the saturation of the SoloVPE detector. To overcome this difference, an alteration in wavelength setting to 615 nm allowed the direct correlation of the slopes between the fixed path length (diluted and measured with a 1-mm cell) and the SoloVPE. The direct correlation of the slopes between technology platforms enabled the certification of the slope from the SoloVPE.

TABLE 8.2 Intermediate Precision of AMG Blue Dye for System Suitability Evaluation 0.15% Patent Blue VF in 1X PBS,

% Glycerol 280 nm 310 nm 510 nm 615 nm

mm) 1.465 3.917 0.474 13.228 A SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.43

3.

0.4

13.

2 1.43

3.

0.4

13.

3 1.43

3.

0.4

13.

4 1.43

3.

0.4

13.

5 1.43

3.

0.4

13.

6 1.43

3.

0.4

13.

7 1.43

3.

0.4

13.

8 1.43

3.

0.4

13.

9 1.43

3.

0.4

13.

10 1.43

3.

0.4

13.

11 1.43

3.

0.4

13.

12 1.43

3.

0.4

13.

B SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.4

3.

0.4

13.

2 1.4

3.

0.4

13.

3 1.4

3.

0.4

13.

4 1.4

3.

0.4

13.

5 1.4

3.

0.4

13.

6 1.4

3.

0.4

13.

7 1.4

3.

0.4

13.

8 1.4

3.

0.4

13.

9 1.4

3.

0.4

13.

10 1.4

3.

0.4

13.

11 1.4

3.

0.4

13.

12 1.4

3.

0.4

13.

C SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.3

3.

0.4

13.

2 1.3

3.

0.4

13.

3 1.3

3.

0.4

13.

4 1.3

3.

0.4

13.

5 1.3

3.

0.4

13.

6 1.3

3.

0.4

13.

7 1.3

3.

0.4

13.

8 1.3

3.

0.4

13.

9 1.3

3.

0.4

13.

10 1.3

3.

0.4

13.

11 1.3

3.

0.4

13.

12 1.3

3.

0.4

13.

D SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.3

3.

0.4

13.

2 1.3

3.

0.4

13.

3 1.3

3.

0.4

13.

4 1.3

3.

0.4

13.

5 1.3

3.

0.4

13.

6 1.3

3.

0.4

13.

7 1.3

3.

0.4

13.

8 1.3

3.

0.4

13.

9 1.3

3.

0.4

13.

10 1.3

3.

0.4

13.

11 1.3

3.

0.4

13.

12 1.3

3.

0.4

13.

E SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.4

3.

0.4

13.

2 1.4

3.

0.4

13.

3 1.4

3.

0.4

13.

4 1.4

3.

0.4

13.

5 1.4

3.

0.4

13.

6 1.4

3.

0.4

13.

7 1.4

3.

0.4

13.

8 1.4

3.

0.4

13.

9 1.4

3.

0.4

13.

10 1.4

3.

0.4

13.

11 1.4

3.

0.4

13.

12 1.4

3.

0.4

13.

F SoloVPE Slopes 280 nm 310 nm 510 nm 615 nm 1 1.4

4.

0.5

14.

2 1.4

4.

0.4

14.

3 1.3

3.

0.4

13.

4 1.4

3.

0.4

13.

5 1.3

3.

0.4

13.

6 1.4

3.

0.4

13.

7 1.4

3.

0.4

13.

8 1.4

3.

0.4

13.

9 1.3

3.

0.4

13.

10 1.4

3.

0.4

13.

11 1.3

3.

0.4

13.

12 1.4

3.

0.4

13.

G SoloVPE Slopes 1 1.4

3.

0.4

13.

2 1.4

3.

0.4

13.

3 1.4

3.

0.4

13.

4 1.4

3.

0.4

13.

5 1.4

3.

0.4

13.

6 1.4

3.

0.4

13.

7 1.4

3.

0.4

13.

8 1.4

3.

0.4

13.

9 1.4

3.

0.4

13.

10 1.4

3.

0.4

13.

11 1.4

3.

0.4

13.

12 1.4

3.

0.4

13.

H SoloVPE Slopes 1 N/A N/A N/A N/A 2 1.4

3.

0.4

13.

3 1.4

3.

0.4

13.

4 1.4

3.

0.4

13.

5 1.4

3.

0.4

13.

6 1.4

3.

0.4

13.

7 1.4

3.

0.4

13.

8 1.4

3.

0.4

13.

9 1.4

3.

0.4

13.

10 1.4

3.

0.4

13.

11 1.4

3.

0.4

13.

12 1.4

3.

0.4

13.

indicates data missing or illegible when filed

Evaluation of AMG Blue Dye as System Suitability Standard

This section discusses the use of AMG Blue dye as the system suitability standard in terms of instrument path length. FIG. 15 shows that the path lengths required for the determinations ranged from the smallest at 0.005 mm for Protein B at 48 mg/mL (Protein B—48) to ^(˜)2.3 mm as the largest path length for the most dilute (1 mg/mL; Protein A). In Table 8.3, the step absorbances (are reported for the proteins from FIG. 15 and standard solutions that are used with the SoloVPE. The large path lengths are required for Protein A due to the low concentration of the protein (1.0 mg/mL). The range of path lengths employed correlated to the range of path lengths used in the AMG Blue dye suitability.

In Slope Spectroscopy™ (SoloVPE), the slope of the line is directly proportional through the extinction coefficient to the concentration. A key attribute of the slope is the amount of light that is permitted to pass through each light slot, therefore sensitivity is based on the absorbance of the individual step in the SoloVPE analysis. The larger the path length (PL) step, the larger the absorbance would be. This absorbance, for an effective system suitability, must be within the SoloVPE detector's capability. If the amount of light is too small, then the detector would be on the edge of failure with each test. If the amount of light is too large in comparison to the protein concentration, then the system suitability lacks sensitivity to detect small variations in the light path and optics of the instrument (i.e. mirror misalignment and linearity wobbles). The step absorbance must be maintained across protein concentrations as determined by the SoloVPE algorithm is preferred.

Example 9—Key Attributes of AMG Blue Dye Standard

The desired attributes of the AMG Blue dye solution were designed to evaluate instrument performance at all concentrations through readings across the AMG Blue dye spectrum as governed by the step absorbance. The current data shows that using the SoloVPE in the Multi-Mode, thereby allowing the SoloVPE algorithm to determine the threshold path length for the sample readings.

Dye Concentration

When analyzing PBD using the SoloVPE in Quick Slope mode, the path lengths are not amenable to high concentration. A more concentrated solution was required. Experiments were conducted to find the optimal concentration of the dye. Patent Blue VF solutions containing 0.1%, 0.12%, 0.15%, 0.2% and 0.5% (w/v) were prepared and tested. Optimal spectral characteristics (^(˜)1 AU at 50 μm) were found at 0.15% w/v.

pH of the Formulation

Patent Blue VF dye is a triphenylmethane family dye. Consequently, the molecule is sensitive to pH changes. The cyclization as shown in Scheme 1 would alter the π-cloud of electrons and therefore alter the color.

If the solution is made incorrectly, the pH and consequently color of the solution in the 0.15% w/v concentrated form could be acidic (i.e. pH 3.2) at which the solution would appear greenish-blue. AMG Blue dye solution at the incorrect pH did not match the fixed path length reading (13.5 abs/mm) but instead showed a slope of 10.5 using the SoloVPE. However, the solution, when buffered to pH 6.8 the solution maintained its blue color and the correlation with the fixed path length instrument.

Organic Composition

Glycerol was used due to the volatility of the methanol in the PBD solution. A concentration of 5% (v/v) was implemented in the AMG Blue dye.

Thus, in summary, the following were observed:

-   -   AMG Blue Dye showed precision at 5% across 6 instruments     -   AMG Blue Dye was 5% from the value using the Fixed Path Length         spectrophotometer at 280 nm, 310 nm, 510 nm, and 615 nm.     -   Readings at 615 nm using the 0.15% (w/v) AMG Blue Dye can         substitute for the reading at 310 nm using the fixed slope.     -   Based on step absorbance measurements, the ConfiRM® standards         are inappropriate for mimicking proteins.

In summary, analyses of data demonstrated that the variability in measurements of the AMG Blue dye solution using six instruments maintained an accuracy of 5% from fixed path length determinations. The concentration of the Patent Blue VF, the pH and organic composition of the AMG Blue dye solution are critical attributes of the AMG Blue solution. Implementation of Multi-Mode for the testing greatly simplifies the system suitability procedure while maintaining the sensitivity required for an effective evaluation of instrument performance.

BIBLIOGRAPHY

-   U.S. Pat. No. 7,808,641 (priority date 2007) INTERACTIVE VARIABLE     PATH LENGTH DEVICE Huffman S, Soni K, Ferraiolo J. 2014. UV-Vis     based determination of protein concentration. BioProcess     International 12: 2-8 -   Sekar, N., 2011, Acid dyes. in Handbook of Textile and industrial     Dyeing (pp. 486-514). Woodhead Publishing.

Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. The use of the singular includes the plural unless specifically stated otherwise. The use of “or” means “and/or” unless stated otherwise. The use of the term “including”, as well as other forms, such as “includes” and “included,” is not limiting. Terms such as “element” or “component” encompass both elements and components comprising one unit and elements and components that comprise more than one subunit unless specifically stated otherwise. The use of the term “portion” can include part of a moiety or the entire moiety. When a numerical range is mentioned, e.g., 1-5, all intervening values are explicitly included, such as 1, 2, 3, 4, and 5, as well as fractions thereof, such as 1.5, 2.2, 3.4, and 4.1.

“About” or “˜” means, when modifying a quantity (e.g., “about” 3 mM), that variation around the modified quantity can occur. These variations can occur by a variety of means, such as typical measuring and handling procedures, inadvertent errors, ingredient purity, and the like.

“Comprising” and “comprises” are intended to mean that methods include the listed elements but do not exclude other unlisted elements. The terms “consisting essentially of” and “consists essentially of”, when used in the disclosed methods include the listed elements, exclude unlisted elements that alter the basic nature of the method, but do not exclude other unlisted elements. The terms “consisting of”and “consists of” when used to define methods exclude substantial method steps. Embodiments defined by each of these transition terms are within the scope of this disclosure.

“Coupled” means associated directly as well as indirectly. For example, a device or process can be directly associated with another device or process, or these devices and/or processes can be indirectly associated with each other, e.g., via another device or process. 

What is claimed:
 1. A method of determining the suitability of a variable-length spectrophotometer for determining protein concentration of a protein sample, comprising measuring the absorbance of Patent Blue dye (PBD) or AMG Blue Dye (ABD) at least two wavelengths, the first wavelength of 280 nm and the subsequent wavelength(s) selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm.
 2. A method of determining the suitability of a fixed path length spectrophotometer for determining protein concentration of a protein sample, comprising measuring the absorbance of ABD at least two wavelengths, the first wavelength of 280 nm and the subsequent wavelength(s) selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm.
 3. The method of claim 1, wherein at least a third wavelength is used, wherein the third wavelength is different than the second wavelength and selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm.
 4. The method of claim 1, wherein the PBD or ABD is measured three times for each wavelength before measuring the protein concentration of the protein sample, and wherein the PBD or ABD is measured three times for each wavelength after measuring the protein concentration of the protein samples.
 5. The method of claim 1, wherein the first wavelength is 280 nm and the second wavelength is 310 nm.
 6. The method of claim 3, wherein the variable-length spectrophotometer is considered suitable if the absorbance readings of the PBD or ABD are equal to or less than 10% of those values supplied in a certificate of analysis supplied with the PBD or ABD.
 7. The method of claim 1, wherein the variable-length spectrophotometer or fixed path length spectrophotometer is considered suitable if the absorbance readings of the PBD or ABD are at least equal to or less than 5% of those supplied in a certificate of analysis supplied with the PBD or ABD.
 8. The method of claim 1, wherein the readings have a relative standard deviation (RSD) percentage of 5%.
 9. The method of claim 1, wherein the protein sample comprises a therapeutic protein.
 10. The method of claim 1, wherein the protein sample comprises an antigen binding protein, an antibody, a bi-specific antibody, a tri-specific antibody, a BiTE molecule, or a fragment or derivative thereof.
 11. The method of claim 1, wherein the variable length spectrophotometer is a SoloVPE spectrophotometer (C Technologies, Inc.; Bridgewater, N.J.).
 12. The method of claim 9, wherein the therapeutic polypeptide is selected from the group consisting of infliximab, bevacizumab, cetuximab, ranibizumab, palivizumab, abagovomab, abciximab, actoxumab, adalimumab, afelimomab, afutuzumab, alacizumab, alacizumab pegol, ald518, alemtuzumab, alirocumab, altumomab, amatuximab, anatumomab mafenatox, anrukinzumab, apolizumab, arcitumomab, aselizumab, altinumab, atlizumab, atorolimiumab, tocilizumab, bapineuzumab, basiliximab, bavituximab, bectumomab, belimumab, benralizumab, bertilimumab, besilesomab, bevacizumab, bezlotoxumab, biciromab, bivatuzumab, bivatuzumab mertansine, blinatumomab, blosozumab, brentuximab vedotin, briakinumab, brodalumab, canakinumab, cantuzumab mertansine, cantuzumab mertansine, caplacizumab, capromab pendetide, carlumab, catumaxomab, cc49, cedelizumab, certolizumab pegol, cetuximab, citatuzumab bogatox, cixutumumab, clazakizumab, clenoliximab, clivatuzumab tetraxetan, conatumumab, crenezumab, cr6261, dacetuzumab, daclizumab, dalotuzumab, daratumumab, demcizumab, denosumab, detumomab, dorlimomab aritox, drozitumab, duligotumab, dupilumab, ecromeximab, eculizumab, edobacomab, edrecolomab, efalizumab, efungumab, elotuzumab, elsilimomab, enavatuzumab, enlimomab pegol, enokizumab, enoticumab, ensituximab, epitumomab cituxetan, epratuzumab, erenumab, erlizumab, ertumaxomab, etaracizumab, etrolizumab, evolocumab, exbivirumab, fanolesomab, faralimomab, farletuzumab, fasinumab, fbta05, felvizumab, fezakinumab, ficlatuzumab, figitumumab, flanvotumab, fontolizumab, foralumab, foravirumab, fresolimumab, fulranumab, futuximab, galiximab, ganitumab, gantenerumab, gavilimomab, gemtuzumab ozogamicin, gevokizumab, girentuximab, glembatumumab vedotin, golimumab, gomiliximab, gs6624, ibalizumab, ibritumomab tiuxetan, icrucumab, igovomab, imciromab, imgatuzumab, inclacumab, indatuximab ravtansine, infliximab, intetumumab, inolimomab, inotuzumab ozogamicin, ipilimumab, iratumumab, itolizumab, ixekizumab, keliximab, labetuzumab, lebrikizumab, lemalesomab, lerdelimumab, lexatumumab, libivirumab, ligelizumab, lintuzumab, lirilumab, lorvotuzumab mertansine, lucatumumab, lumiliximab, mapatumumab, maslimomab, mavrilimumab, matuzumab, mepolizumab, metelimumab, milatuzumab, minretumomab, mitumomab, mogamulizumab, morolimumab, motavizumab, moxetumomab pasudotox, muromonab-cd3, nacolomab tafenatox, namilumab, naptumomab estafenatox, narnatumab, natalizumab, nebacumab, necitumumab, nerelimomab, nesvacumab, nimotuzumab, nivolumab, nofetumomab merpentan, ocaratuzumab, ocrelizumab, odulimomab, ofatumumab, olaratumab, olokizumab, omalizumab, onartuzumab, oportuzumab monatox, oregovomab, orticumab, otelixizumab, oxelumab, ozanezumab, ozoralizumab, pagibaximab, palivizumab, panitumumab, panobacumab, parsatuzumab, pascolizumab, pateclizumab, patritumab, pemtumomab, perakizumab, pertuzumab, pexelizumab, pidilizumab, pintumomab, placulumab, ponezumab, priliximab, pritumumab, PRO 140, quilizumab, racotumomab, radretumab, rafivirumab, ramucirumab, ranibizumab, raxibacumab, regavirumab, reslizumab, rilotumumab, rituximab, robatumumab, roledumab, romosozumab, rontalizumab, rovelizumab, ruplizumab, samalizumab, sarilumab, satumomab pendetide, secukinumab, sevirumab, sibrotuzumab, sifalimumab, siltuximab, simtuzumab, siplizumab, sirukumab, solanezumab, solitomab, sonepcizumab, sontuzumab, stamulumab, sulesomab, suvizumab, tabalumab, tacatuzumab tetraxetan, tadocizumab, talizumab, tanezumab, taplitumomab paptox, tefibazumab, telimomab aritox, tenatumomab, tefibazumab, teneliximab, teplizumab, teprotumumab, tezepelumab, TGN1412, tremelimumab, ticilimumab, tildrakizumab, tigatuzumab, TNX-650, tocilizumab, toralizumab, tositumomab, tralokinumab, trastuzumab, TRBS07, tregalizumab, tucotuzumab celmoleukin, tuvirumab, ublituximab, urelumab, urtoxazumab, ustekinumab, vapaliximab, vatelizumab, vedolizumab, veltuzumab, vepalimomab, vesencumab, visilizumab, volociximab, vorsetuzumab mafodotin, votumumab, zalutumumab, zanolimumab, zatuximab, ziralimumab, zolimomab aritox, a glycoprotein, CD polypeptide, a HER receptor polypeptide, a cell adhesion polypeptide, a growth factor polypeptide, an insulin polypeptide, an insulin-related polypeptide, a coagulation polypeptide, a coagulation-related polypeptide, albumin, IgE, a blood group antigen, a colony stimulating factor, a receptor, a neurotrophic factor, an interferon, an interleukin, a viral antigen, a lipoprotein, calcitonin, glucagon, atrial natriuretic factor, lung surfactant, tumor necrosis factor-alpha and -beta, enkephalinase, mouse gonadotropin-associated peptide, DNAse, inhibin, activing, an integrin, protein A, protein D, a rheumatoid factor, an immunotoxin, a bone morphogenetic protein, a superoxide dismutase, a surface membrane polypeptide, a decay accelerating factor, an AIDS envelope, a transport polypeptide, a homing receptor, an addressin, a regulatory polypeptide, an immunoadhesin, a myostatin, a TALL polypeptide, an amyloid polypeptide, a thymic stromal lymphopoietin, a RANK ligand, a c-kit polypeptide, a TNF receptor, and an angiopoietin, the antibodies shown in Table 1 and biologically active fragments, analogs or variants thereof.
 13. The method of claim 2, wherein at least a third wavelength is used, wherein the third wavelength is different than the second wavelength and selected from the group consisting of 310 nm, 412 nm, 510 nm and 615 nm.
 14. The method of claim 2, wherein the PBD or ABD is measured three times for each wavelength before measuring the protein concentration of the protein sample, and wherein the PBD or ABD is measured three times for each wavelength after measuring the protein concentration of the protein samples.
 15. The method of claim 2, wherein the first wavelength is 280 nm and the second wavelength is 310 nm.
 16. The method of claim 2, wherein the variable-length spectrophotometer or fixed path length spectrophotometer is considered suitable if the absorbance readings of the PBD or ABD are at least equal to or less than 5% of those supplied in a certificate of analysis supplied with the PBD or ABD.
 17. The method of claim 2, wherein the protein sample comprises a therapeutic protein. 